The invention relates to a device for arranging in a liquid conduit for limiting a liquid flow in this conduit.
Good-quality drinking-water can be obtained by treating water obtained by means of surface abstraction (rivers and lakes) and depth abstraction (groundwater). When the water has been purified to good-quality drinking-water, it must then be transported to the customer. This transport is very expensive because of the very finely branched supply system. Groundwater abstraction has the further drawback that the groundwater level falls through the abstraction of the water, and this can have adverse consequences for the environment.
Saving good-quality drinking-water is a good idea in order to prevent, among other things, a fall in the groundwater level and to reduce the consumption of energy for transport, purification and heating.
Water utility companies attempt to reduce the consumption of good-quality drinking-water in three ways. First of all, efforts are made to make the mains system as watertight as possible. Secondly, water-saving equipment is used and rainwater can for instance be used to do the washing, for the toilet and to water the garden. Thirdly, taps which are not used specifically for drawing a quantity of water, such as the tap of a wash-basin, are provided with a device as stated in the preamble. With such a device as according to the preamble the flow rate of such taps is limited to about 7-8 litres per minute.
NL-A-1001810 describes a flow limiter which comprises a hat-shaped part, wherein two slots are arranged in the upper side of the part. These slots bound a flexible bridge part which bends under the influence of the pressure difference over the hat-shaped part such that the slots are made smaller. This device has the drawback that due to the small dimensions of the gaps the operation of the device is adversely affected by small variations, for instance due to swelling of the material. This device has the further drawback that during limiting of warm or hot liquid flows the device deforms, whereby the operation is adversely affected. Because of the geometry of the bridge part it is moreover not possible to manufacture the device at a reasonable cost. In addition, it is extremely difficult to find a combination of material properties and shape and dimensions wherein the device functions over the whole operating range.
It is an object of the invention to prevent the above stated drawbacks.
It is a further object of the invention to provide a device which limits the flow such that the flow rate remains virtually the same irrespective of the pressure of the supply.
The above stated objectives are achieved with a device according to the invention, which device comprises a base part with a through-flow opening and a closing part which is arranged on the base part via spring means and which is displaceable with at least a substantial axial component for partially closing the through-flow opening against a closing surface on the base part, wherein the device can be fixed at a fixed position in the conduit by means of fixation means such that the liquid can pass through the device only via the through-flow opening and wherein the base part and the closing part are arranged relative to each other such that in a rest position defined by the spring means a gap is formed between the base part and the closing part, which gap is made smaller counter to the spring action by bending under the influence of the liquid pressure difference over the device.
An advantage of a device according to the invention is that the closing part closes off the through-flow opening as far as necessary and the size of he gap depends on the liquid pressure difference. The relation between the closing part and the liquid pressure difference results in practically the same outflow being obtained irrespective of the supply pressure of the liquid. In a preferred embodiment of the invention the base part comprises an annular flange part and a standing wall along the inner periphery of the annular flange part, and the closing part is arranged on the end of the wall remote from the annular flange part. This embodiment can be readily incorporated into a conduit and because the base part comprises an annular flange part the liquid can flow easily through the gap without the liquid encountering resistance from the base part.
In another embodiment of the invention the gap is wedge-shaped. This embodiment of the gap results in a very preferred limiting characteristic.
In yet another embodiment of the invention the gap comprises a constriction on both ends. A practically constant flow rate is hereby obtained over the whole operating range of the device.
In another preferred embodiment of the invention the flexible part comprises a plate part and at least one spring element connecting the plate part to the base part. The flow-limiting characteristic is hereby determined wholly by the spring element. The preferred limiting characteristic is obtained by a suitable choice of the spring characteristic of the spring element. The spring element is preferably helical.
In yet another embodiment the device is monolithic. The device is herein preferably manufactured by injection moulding, whereby the cost can be kept low.
In yet another embodiment of the device the closing surface comprises a protrusion for preventing complete closure of the gap. This prevents the device closing the conduit completely if the liquid pressure rises too high.
In another further embodiment the device comprises an opening for ensuring a minimal flow. This likewise prevents the gap from being completely closed by the closing part in the case of too high a liquid pressure.
In a preferred embodiment of the device the gap opening extends in radial direction. The advantage hereof is that a back-pressure is created under the closing part, whereby bending of the closing part progresses in smooth and damped manner as the pressure rises.
In yet another embodiment of the device the gap has a stepped wedge shape. The choking action of the device will hereby proceed in two stages. The first stage can thus be adapted to the requirements for a constant flow rate at a low pressure. The second stage can then be adapted to the requirements for a constant flow rate at high pressure.